On the Stomatal Frequency in Barley. : I. The Relationship between Stomatal Frequency and Photosynthesis

Abstract

The relationship between stomatal frequency and photosynthesls in barley was studied to determine whether stomatal Lrequency can be used to screen plants for high photosynthetic ca pacity. Photosynthesis and transpiration of 7 cultivars differing in stomatal frequency were measured (Table 1). The analysis of variance (Table 2) revealed that these cultivars differed significantly in stomatal frequency and photosynthesis but not in transpiration. There was a positive correlation between stomatal frequency and photosynthesis, r=0.94 and also between stomatal frequency and transpiration, r=0.86 (Fig. 1). The coefficient of regression of photosynthesis on stomatal frequency was 0.207, which indicated that the increase of one stoma per mm2 resulted in the increase of 0.207 CO2 mg/dm2/hr intake. By Gaastra's equation, the resistance of the air (ra), the stomata (rs), and the mesophyll (rm) to the diffusion of CO2 and the resistance of the air (ra'), and the stomata (rs') to the diffusion of H2O were computed (Table 3). Stomatal resistance tended to decrease as stomatal frequency increased (Fig.2). Mean (rs')/mean (ra'+rs)=0.60 and mean (rs)/ mean (ra+rs+rm)=0.16. It appears that transpiration was more affected by the change of rs' than photosynthesis. But the correlation between stomatal frequency and mesophyll resistance was -0.93. This indicates that mesophll resistance was affected by changes in stomatal frequency whose effect was not wholly separated by Gaastra's equation.